The embodiments described herein relate generally to electric motors, and more particularly, to an electric motor and methods of manufacture.
At least some known heating, ventilating and air-conditioning (HVAC) systems utilize multi-speed permanent split capacitor (PSC) motors. In general, a multi-tapped PSC motor is a motor that includes a multi-tapped main winding where all or part of a series-coupled main winding and one or more boost windings are coupled in parallel to a series-coupled start winding and capacitor. Such multi- speed PSC motors are used in HVAC applications, such as furnace blower and air handler applications, because the one or more boost windings may be energized to produce multiple levels of output torque and, therefore, multiple levels of output speed to deliver different amounts of air flow for different applications. For example, one tap setting may provide a relatively low amount of air flow for air circulation when there is no heating or cooling activity. Another tap setting could increase the air flow when cooling is desired. By using multiple taps, various operating states can be established for a PSC motor, such as heating, cooling, and air. In general, each tap point on the multi-tapped PSC motor is coupled to an input line and a switch is energized in response to control signals from, for example, a system controller to energize one of the tap points at any given time.
The maximum operating efficiency of a PSC motor is typically obtained by operating the motor at full load, so a reduced HVAC system load results in inefficient operation of the PSC motor. The HVAC system load may be reduced because of varying demand cycles due to a variety of factors such as, for example, daily and seasonal fluctuations of ambient temperature, human activity in the controlled environment, and intermittent operation of other equipment in the controlled environment. The start winding and capacitor are designed to optimize efficiency when operating in a high-speed operating mode such as a nominal AC line input frequency, e.g., 60 Hz. As a result, operation of the PSC motor at other than the nominal frequency results in production of less than optimal torque and inefficient operation. Moreover, efficiency standards are becoming stricter for medium-speed operating modes, which are sometimes used as much or more than high and low-speed operating modes.